1. Field
The present embodiments relate to optical connections and, more particularly, to optical connections between microchips.
2. Brief Description of Related Developments
Large symmetric multiprocessor machines such as blade servers are running out of bandwidth for blade-to-blade, module-to-module and eventually chip-to-chip interconnections. The bandwidth required for these interconnections is growing more rapidly than Moore's law because this bandwidth is the product of the increasing number of processors, the increasing complexity of each processor and the increasing clock speed of those processors. In order to build a complete optical interconnection hierarchy several levels of connections should be addressed. The optical signal travels from the chip to the module, from the module to the board, from the board to the backplane, across the backplane and then back through these levels in the reverse order.
In conventional mainframe and high-end applications, chips interconnect via a substrate using controlled collapse chip connection (C4 or flip chip) bonding. The substrate may be, for example, a glass ceramic multichip module or silicon interposer. Chip to chip electrical connections flow from a chip through the C4 interconnect to the multichip module and then back through the C4 interconnect to the next chip. These C4 electrical connections are not sufficient to accommodate the necessary increase in bandwidth.
Existing optical connections rely on multimode waveguides or multimode fibers because the large cores of multimode waveguides do not require tight mechanical tolerances during assembly, the losses within the short range between chips is negligible and the sources are often multimode. These existing optical connections use volume holographic gratings that are not a feasible manufacturing approach to the problem of the increasing bandwidth requirements because these volume holographic gratings cannot be easily created using microlithography.
It would be advantageous to replace some of the chip to chip electrical connections with easily manufactured optical connections to allow higher speeds over chip to chip distances.